1. Field of the Invention
This invention relates to a process for the production of malonic acid dinitrile from acetonitrile and cyanogen chloride in the gaseous phase and purification thereof.
U.S. Pat. No. 2,553,406 discloses that malonic acid dinitrile can be obtained by reacting acetonitrile and cyanogen chloride for a period of from 5 to 15 seconds at a temperature above 600.degree. C. and preferably at a temperature of from 650.degree. to 700.degree. C. According to the example, the yields amount to less than 18%. It is also stated in this patent that the yields are reduced even further by exceeding 700.degree. C.
U.S. Pat. No. 2,606,917 explains that where high temperatures are used, the reaction is accompanied both by decomposition and by the separation of carbon and polymers. According to this patent, the disadvantages can be avoided by using an inert gas. Unfortunately, the use of an inert gas does not provide an improvement in the poor yield of malonic acid dinitrile. Example 7 teaches a yield of only 16.8% is obtained at a reaction temperature of 650.degree. C. for a duration of 6 seconds with a cyanogen chloride to acetonitrile to carbon dioxide molar ratio of 1:3:7.2.
Japanese Patent Publication 16506/66 discloses the yields are improved by introducing a small quantity of chlorine as catalyst into the gaseous reaction components i.e. acetonitrile and cyanogen chloride. The yields are thereby improved to approximately 70%. However, the use of chlorine as a catalyst results in the formation of large quantities of fumaric acid dinitrile and maleic acid dinitrile as by-products. This is particularly disadvantageous because maleic acid dinitrile is extremely difficult to separate from malonic acid dinitrile. In addition, the use of chlorine causes a considerable expense for apparatus.
The malonic acid dinitrile reaction product of acetonitrile and cyanogen chloride contains as contaminating by-products fumaric acid dinitrile and maleic acid dinitrile. The removal of these by-products from the reaction mixture involves considerable difficulty because of similarities in the physical constants.